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All at sea in a flat botom boat.


Indications are that sooner rather than later I'll be all at sea in a flat bottom boat.

In pursuit of such nautical means it helps to have a neighbour who:
  • has a workshop with tools
  • is retired
  • began working life as an apprentice boat builder then after years in the Navy  air arm,  built gliders out of wood.
  • unlike me, can read a set of plans.
How I even imagined  I could build this myself I don't know  as my carpentry skills and chippy experience are zilch. 

But there you go: geographical happenstance in da hood. 

Flat bottom boating is an interesting aspect of water transport. There are many examples world wide of flat bottoms being preferred to curvy ones: barge, bateau, flatboat, gondola, jon boat, keelboat, pirogue, pram, punt, scow and Trow, etc.

My favorite flat bottom canoes are the Aitutaki in the Cook Islands. Simple. Functional.They're polled -- punted (pushed along by a big stick along the water bottom)--  and I like to punt. 

The advantage with the horizontal underneath is that you are less likely to run aground and your deck is more stable in flat water than with a curved hull. So standing up is allowed. 

I'm using a brilliant Michal Storer design. Michael is an Australian  boat designer and builder who has a dedicated following internationally, esp in the US. 

The design templates a lot of use out of just three pieces of plywood.

But flat bottom?

My intended use is in very shallow coastal waters and estuaries. Tidal creeks. As the tide falls I'll have to manoevre over many sand bars. I also don't expect a lot of wave traffic..
I'll be adding sail and that should be interesting. I know the sail rig works fine as I've used it on my beamy plastic kayak --  but if I'm gonna be tip prone I may have to add an outrigger or maybe a leeboard.

But I'm thinking that going without these add ons makes for a more challenging sailing adventure.

With a length of 4.7m (15ft 6ins) and weight of  23kg my flat bottom boat -- it's a canoe (design pictured right) --  fits my requirements very well indeed. (It looks stylish, don;t you think?)
  • a two people, two dog, watercraft
  • plenty of space to carry stuff -- indeed a lot of stuff.
  • big enough to stow away a sail.
  • long enough to sail without having to add extra bits. Really a sailing canoe has to be at least over 12 feet long. That's something I've learnt from my own messing about.
  • "easy", cheap and quick to build.
As for flat versus V here's an interesting discussion from Voyager canoes about stability:
The flat bottom will tend to remain parallel to the surface of the water, and just below it, (unless you are carrying a very large number of helium balloons).  If you are canoeing on calm, flat water, then the flat bottom will make for a much more stable ride.  You can shift your weight to greater extremes and not feel that the canoe will rotate under you and tip you out.
Another way to look at it, is that it is easier to keep your centre of gravity over the flatter boat whereas the rounder hull seems to slip out from under you, leaving your centre of gravity over the edge.
If you are in rougher water, the situation is more complex:
If you are on the side of a wave, the water surface, and thus the flat bottom of the boat, may be tipped at a considerable angle.  If you are sitting perpendicular to the bottom, then you might find it very difficult to keep your centre of gravity over the boat. (Depending on the severity of the wave and the height of your seat)
The round bottom boat will tend to rotate so that the water is higher on one side than the other, but it means that you will find it easier to remain vertical and keep your centre of gravity over the boat.
If the boat takes on water, the water will form a shallow layer across the entire bottom of the flat bottom boat, but it will tend to concentrate and be deeper, down the centre line of the rounder boat.
In flat water, this means you have a greater variety of depths of water to place your feet in, which may not be of much concern to you or your feet.
In rough water, the deeper water around the centre line will tend to pull the centre of the boat down, rotating the boat to keep the bottom down.  This will tend to keep the paddler above the centre line of the canoe and in a reasonably vertical position.
As the flat bottom boat tips with the surface of the wave, the shallow pool will suddenly rush to the lower side, and the weight and momentum of it will increase the tendancy to tip.  As the boat goes over the wave and tips the other way, the water will suddenly surge to the other side.
The momentum of the water will act to enhance the extremes of the boat motion which will force you into a position that continually places your centre of gravity beyond the edges of the boat.  This, of course, increases the likelihood that you will get to use the PFD that you so-wisely are wearing.
The water in the round boat will also oscillate around the centre point, but due to the shape of the hull, the oscillations will not be as severe and the boat will have a greater tendancy to keep its occupants in stable positions.
In reality you will select a canoe that best suits how you will use it, and it will likely be a compromise shape, between the extremes.  If like me, you like to glide through the backwaters on a calm day and examine the flora and fauna beneath you, you will select a flatter canoe.  If you like more adventure, or perhaps you want more speed, then you will want a different style.
The accompanying diagrams are HERE.











 

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